In recent years there has been considerable interest in carpet tiles. Carpet tiles offer considerable advantages over rugs or wall to wall carpeting which has heretofore been used extensively. For example, the use of carpet tiles for floor covering allows removal of individual tiles which have become worn or soiled more than other tiles. Those tiles which are not worn or soiled may be left in place. Additionally, tiles may be rearranged or replaced to enhance decorative effects.
Carpet tile and carpet construction are, of course, well-known in the art and are shown, for example, in U.S. Pat. Nos. 3,402,094; 3,347,735; 3,764,448; 3,238,595; 2,776,233; 3,173,823; 3,309,259; 3,320,113; 3,515,622; 3,642,516; 3,120,083; and 3,014,829. In addition, carpet tiles of various constructions have been available commercially.
Generally, carpet tiles as known heretofore have included a pile fabric facing set in a layer of resilient thermoplastic (including elastomeric) material which is stiffened with a layer of suitable stiffening fibers such as of glass, polypropylene, nylon or the like. The tile is generally backed with another layer of resilient elastomeric or thermoplastic material to which an adhesive may be applied to set the carpet tile onto the floor. Commercially available carpet tiles are available with an adhesive applied on the backing and a strippable protective layer attached thereto. In use, the protective layer is stripped off and the carpet tile applied to the floor surface. While the known carpet tile constructions offer many advantages over conventional rugs, wall to wall carpeting or the like, many problems remain.
Dimensional stability is important in a carpet tile. Dimensional stability, as understood in the art, is the ability of a carpet tile to lie flat and remain flat and square on a floor surface under conditions of normal use. To achieve commercially acceptable dimensional stability, particularly dimensional stability under concentrated stress (as when a wheeled object such as a desk chair, couch, typewriter stand or the like, traverses a floor composed of a plurality of carpet tiles), it has generally heretofore been necessary to adhere the carpet tiles to the floor with a suitable adhesive. The use of an adhesive, however, diminishes the advantageous features of carpet tiles as compared with rugs or wall to wall carpeting. An adhesive-installed tile requires substantial time and effort to remove or replace an individual tile. When the carpet tile is backed with an adhesive layer, it is often difficult to precisely align the carpet tile since the tile sticks to the floor surface as soon as it is placed in contact therewith.
Tiles which are not adhesively adhered to the floor (known as free-lay tiles) have heretofore been too dimensionally unstable, particularly when subjected to concentrated stress, to be commercially practical. It has been proposed to prestress the carpet tiles during manufacture to overcome the dimensional stability problem. A pre-stressed carpet tile of this type can be manufactured, for example, with a dome-type of orientation in which the center of the tile is slightly higher than all of the corners. This construction is purported to reduce dimensional instability, particularly under concentrated stress. It has been found, however, that carpet tiles of this type do not lie flat and tend to form exaggerated domes in use. This different type of dimensional instability also makes this type of carpet tile commercially unsatisfactory.
Another important consideration is the flame retardant and smoke emission characteristics of the carpet tile. Commercially available carpet tile products are subjected to the stringent flame retardant and smoke characteristics requirements set forth in ASTM E-84. It has been suggested to utilize a glass fabric material both for the backing and for the pile surface in order to meet these rigid requirements. See, for example, U.S. Pat. No. 3,764,448. While an all glass fabric may satisfy these flame and smoke requirements, glass fibers are often irritating to humans and thus not particularly suitable for use in such a situation in which the fiberglass fiber would be expected to come in contact with human skin. In addition, glass filaments are known to be relatively stiff, brittle and self abrasive. Their use makes processing and formation of carpet material more difficult. Carpet and/or carpet tile manufacturers thus tend to minimize the use of glass fibers as much as possible.